Learning to speak was the most remarkable thing you ever did. It wasn’t just the 50,000 words you had to master to become fluent or the fact that for the first six years of your life you learned about three new words per day. It was the tenses and the syntax and the entire scaffolding of grammar, not to mention the metaphors and allusions and the almost-but-not-quite synonyms.

But you accomplished it, and good for you. Now imagine doing it two or three times over — becoming bilingual, trilingual or more. The mind of the polyglot is a very particular thing, and scientists are only beginning to look closely at how acquiring a second language influences learning, behavior and the very structure of the brain itself. At a bilingualism conference last weekend convened by the Lycée Français de New York, where all students learn in both English and French, and the…